The invention relates to a device for dispensing fluids from a sealed storage container.
Conventional devices for dispensing pharmaceuticals are known. Metering pumps of this type permit the delivery of a defined quantity of a fluid from a storage container.
EP-O 739 247 B1 describes a metering pump without equalization of air which is intended for the spraying of liquids whose working life is reduced on contact with atmospheric oxygen. The known metering pump has a pressure cylinder which protrudes into the fluid container and in which a piston having an axial pump channel is guided in a sealing manner. A pressure chamber is formed in the pressure cylinder, said pressure chamber being bounded by the piston and by a ball valve, which acts relative to the fluid container and closes when there is positive pressure and opens when there is negative pressure, and being connected to the axial pump channel. The piston is kept in the upper rest position by spring force. When the piston is pressed downward, the pressure in the pressure chamber increases, the valve to the fluid container is closed and the liquid present in the pressure chamber escapes under pressure to the outside through the axial pump channel. When the piston is released, a negative pressure arises in the pressure chamber, with the result that the valve to the fluid container opens and liquid is drawn into the pressure chamber. Since the metering pump operates without equalization of air, the fluid container contains an inner bag which is sealed with respect to the atmosphere and collapses when the fluid container is emptied.
During filling of the metering pumps not having equalization of air, residual air remains in the inner bag. During storage the fluid is therefore constantly in touch with atmospheric oxygen, which leads to a reduction in the storage life or the freedom of the liquid from germs. However, emptying of the fluid container in a germ-free atmosphere or under protective gas is very complex and expensive. Moreover, complete emptying of the bag is only possible when no residual air remains in the bag after it has been filled.
EP-O 739 247 B1 therefore proposes drawing off the residual air via the axial pump channel. In order to provide a connection to the inner bag, openings are provided in the pressure cylinder. Furthermore, the piston is guided in a sealing manner by a circumferential sealing lip only over part of the pressure cylinder. In a certain position of the piston, the residual air from the bag can therefore be drawn off via the openings in the pressure cylinder, the gap between the inner wall of the pressure cylinder and the outer wall of the piston into the pressure chamber and from the pressure chamber via the axial pump channel. In order to prevent liquid from passing into the pressure chamber when a negative pressure is applied, the valve acting relative to the bag has to be closed. This takes place by means of a tappet which is introduced into the piston when the residual air is drawn off.
The known method has been tried and tested in practice. However, it is disadvantageous that, in order to draw off the residual air, the ball valve acting relative to the fluid container has to be closed by means of the tappet. There is the risk here of the tappet jamming the ball of the ball valve. This can only be prevented by very great dimensional accuracy which leads to a higher outlay on production. Moreover, the creation of the connection between the bag and pressure chamber is also associated with an increased outlay on production. Otherwise, it is disadvantageous that the protective cap has to be removed from the metering pump in order to be able to connect a suction pump to the pump channel.
The invention is therefore based on the object of providing a device for dispensing fluids from a sealed storage container, in which the removal of residual air is possible in a particularly simple manner.
This object is achieved by the features of patent claim 1.
The residual air in the storage container is not drawn off via the axial pump channel, but rather via a passage which is formed between the outer wall of the piston and the inner wall of the pressure cylinder above the opening in the pressure cylinder. In order to close the passage, means are provided which are created in such a manner that residual air can be drawn off from the storage container via the passage when a negative pressure is applied, but otherwise the passage is closed. Since the residual air is not drawn off via the axial pump channel, the protective cap does not need to be removed from the dispensing device.
In a preferred embodiment, the passage between the piston and pressure cylinder leads into a space which is to be charged with negative pressure and is formed in the housing body. In order to draw off the residual air, a vacuum pump for producing the negative pressure is connected to the housing body.
The means for closing the passage are preferably designed as a sealing washer with a circular recess in which the piston is guided in a sealing manner. A sealing washer of this type, which preferably consists of polyethylene, can be inserted into the housing body without a relatively great outlay in terms of manufacturing.
The passage for drawing off the residual air between the piston and pressure cylinder is preferably a gap, i.e. the piston is not guided in a sealing manner in this region of the pressure cylinder. However, it is also possible, instead of a gap, to provide grooves or the like running longitudinally in the inner wall of the pressure cylinder and/or the outer wall of the piston.
One or more openings can be provided in the pressure cylinder in order to draw off the air. The openings in the pressure cylinder are preferably slots distributed around the circumference.
In a further preferred embodiment, the housing body has two housing parts with a respective cylindrical section which can be displaced relative to each other in order to actuate the piston. These two housing parts preferably enclose the space to be charged with negative pressure and are preferably sealed relative to each other when they are compressed, with the result that the piston is advanced into the pressure chamber. However, the cylindrical sections of the two housing parts may also be sealed relative to each other with an annular seal or the like in such a manner that a negative pressure can also build up in the space enclosed by the two parts when the piston is not in the advanced position.
The piston is sealed below the opening in the rotary cylinder preferably only by a circumferential sealing lip at the lower end of the piston, the pressure cylinder being extended, for venting purposes, in a region at the lower end of the pressure chamber in such a manner that the sealing action of the sealing lip is lost in this region.
In order to be able to draw off the residual air via the passage, the two housing parts of the housing body are compressed, with the result that the piston is advanced into the pressure chamber. In this position, the two housing parts are sealed relative to each other, and the sealing lip of the piston is sealed with respect to the pressure cylinder. In this case, the sealing lip bears in a sealing manner against the inner wall of the pressure cylinder below the extension of the latter. Below the extension, the sealing lip can also rest on a step of the pressure cylinder which forms a lower stop for the piston. The effect achieved by sealing the piston with respect to the pressure chamber is that, when the residual air is drawn off, the axial pump channel is closed, with the result that liquid cannot be drawn out of the container.
Since the pump channel is closed by the piston when drawing off the residual air, the valve acting relative to the storage container does not need to be closed by means of a tappet or the like, this increasing the outlay in terms of manufacturing due to the high dimensional accuracy.
The housing body can be fastened to the storage container, in particular a glass or plastic bottle, by means of a clamping or screw fastening.